In UMTS (Universal Mobile Telecommunications System) networks, for the purpose of improving spectral efficiency and further improving data rates, by adopting HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access), it is performed exploiting maximum features of the system based on W-CDMA (Wideband Code Division Multiple Access). For the UMTS network, for the purpose of further increasing high-speed data rates, providing low delay and the like, Long Term Evolution (LTE) has been studied (Non-patent literature 1). In LTE, as a multiplexing scheme, OFDMA (Orthogonal Frequency Division Multiple Access) different from W-CDMA is used in downlink, and SC-FDMA (Single Carrier Frequency Division Multiple Access) is used in uplink.
In the 3G system, a fixed band of 5 MHz is substantially used, and it is possible to achieve transmission rates of approximately maximum 2 Mbps in downlink. Meanwhile, in the LTE system, using variable bands ranging from 1.4 MHz to 20 MHz, it is possible to achieve transmission rates of maximum 300 Mbps in downlink and about 75 Mbps in uplink. In the UMTS network, for the purpose of further increasing the wide-band and high speed, successor systems to LTE have been studied (for example, LTE Advanced (LTE-A)).
In the LTE system and LTE-A system, studied is a radio communication system in which a small-scale cell having a local coverage area is disposed in a large-scale cell having a wide-range coverage area. Such a radio communication system is also called the HetNet (Heterogeneous Network).